“We are hoping the extension will be fruitful,” said Susan Henshaw Jones, the City Museum’s president, who has been running both institutions.

But the situation doesn’t look promising. Because the water surged to six feet at the lobby entrance, the building’s electrical systems have not been fully restored. “Post-Sandy, we are struggling,” Ms. Jones said. “We can’t keep the galleries open.”

In dire financial straits, the Seaport Museum was rescued by the City Museum in 2011. A $2 million grant from the Lower Manhattan Development Corporation gave the City Museum up to 18 months to see if it could make a go of the Seaport museum. Counting a six-month extension, that interim period expires this month.

“The terrific leadership of President Susan Henshaw Jones and the entire board and staff has guided the organization through a challenging time,” Kate D. Levin, the New York City cultural affairs commissioner, said in a statement.

This is a more complete version of the story than the one that appeared in print.